Embodiments of the present specification relate generally to interventional procedures, and more particularly to methods and system for improved broadband intravascular ultrasound imaging.
Interventional techniques are widely used for managing a plurality of life-threatening medical conditions. Particularly, certain interventional techniques entail minimally invasive image-guided procedures that provide a cost-effective alternative to invasive surgery. For example, intravascular ultrasound (IVUS) imaging may be used for diagnosing and/or treating diseased blood vessels using image-derived information. Specifically, IVUS imaging may be used to ascertain existence and progression of atherosclerosis plaques, narrowing of the lumen, and/or intracoronary thrombosis that may lead to a heart attack, stroke, and/or cardiac death.
Generally, IVUS imaging systems used in such diagnoses employ a miniaturized ultrasound probe including a catheter having a diameter of less than about 1.2 millimeter (mm). The IVUS catheter may be inserted into, or proximal, a region of interest (ROI) such as a coronary vessel for visualizing structural aspects of the vessel in offline or real-time mode. Particularly, the IVUS catheter may include an imaging sensor such as a side-looking ultrasound transducer that may be used to generate cross-sectional images from within the vessel.
Conventional ultrasound transducers used for generating the cross-sectional images operate between center frequencies of about 20 MegaHertz (MHz) and about 45 MHz with an imaging bandwidth approximately between 30-50 percent. However, conventional ultrasound transducers may provide insufficient resolution for imaging specific features of a subject. For example, use of the center frequencies between 20-40 MHz and the imaging bandwidth between 30-50 percent may provide insufficient resolution for evaluating the vulnerability of atherosclerotic plaques with relatively thin fibrous caps, for example, having a thickness of less than approximately 64 micrometers (μm).
Accordingly, an ultrasound transducer having higher resolution may be preferred to diagnose diseased regions of a patient. However, IVUS imaging resolution is inversely proportional to a frequency bandwidth of the transducer. Typically, a transducer with broad bandwidth and higher working frequency is able to generate short ultrasonic pulses that are useful in distinguishing close targets in an axial direction. However, use of higher frequencies results in higher ultrasound attenuation, which in turn, results in lower penetration depth. Alternatively, a transducer operating at lower frequencies may provide greater penetration depth, but may not provide sufficient image resolution.
Conventional interventional procedures, thus, may entail use of different ultrasound transducers, one or more of which may operate at high frequencies to provide images having higher resolution, while others operate at lower frequencies to provide greater penetration depth. Alternatively, additional imaging modalities such as optical coherence tomography system or a fluorescence system may be employed to determine either high resolution or depth-based information. Use of different imaging modalities and/or different ultrasound transducers, however, prolongs imaging time, while adding to the equipment and operational costs. Furthermore, integrating two different transducers to the tip of a catheter having less than 1 mm diameter causes complicated packaging problems.